In medical image processing, the image registration may refer to the process of performing certain spatial transformation on an image, so as to facilitate comparisons of images of an object taken at different times or stages of a disease as it progresses. The image registration may be widely used for the purposes of medical diagnosis and treatment. The image registration may aid doctors in visualizing and monitoring pathological changes in an identical object over time. For example, the image registration may help doctors monitor the growth or shrinkage of a lesion or nodule and may aid in detecting subtle changes in the density of the lesion or nodule over time. Thus, it is desirable to improve the accuracy of image registration in medical images.